Sprocket and chain gearing are commonly employed for power transmission in heavy equipment and machinery, such as armored face conveyors incorporating chain/flight conveying systems for coal or the like. Such conveyors typically run in one direction substantially all the time conveying the coal from a coal face to a delivery station. There the coal is transferred to the tailpiece of a takaway conveyor or other coal transporting equipment.
It should be appreciated that armored face conveyors operate in a harsh environment while conveying heavy loads of the coal or other won aggregate material. Since these conveyors are operated in substantially one direction all the time, the load bearing or driving faces of the sprocket teeth that drive the chains are subjected to a high degree of wear. Once worn, the drive sprocket must be replaced to ensure proper conveyor operation.
It should be recognized, however, that the reverse side or trailing faces of the sprocket teeth are subjected to little force and little or no wear. Accordingly, these surfaces are essentially like new when the drive faces are worn out and the sprocket is replaced. Prior art sprocket designs for armored face conveyors have, however, failed to take this into consideration. In fact, the sprockets have been constructed with an integral shoulder at one end of the central bore that effectively prevents reversibility.
The present invention recognizes the untapped resource represented by the trailing faces of the teeth and takes advantage of it to essentially double the service life of a drive sprocket. More particularly, the drive sprocket assembly of the present invention is designed to be reversible. Accordingly, when the original driving faces of the sprocket teeth become worn, the sprocket is first disassembled from the conveyor drive shaft. The orientation of the sprocket is then reversed and the sprocket is reassembled on the conveyor drive shaft. The previous, unworn trailing faces of the sprocket teeth thereby become the new drive faces for engaging and driving the chains. Thus, it should be appreciated that replacement of the sprocket is not necessary until both sides of the sprocket teeth become fully worn.
The desirability of providing reversible sprockets has been recognized in the art before. The proposed solutions, however, have not been fully acceptable. For example, in U.S. Pat. Nos. 1,921,329 to Smoot and 4,308,019 to Horkey et al., sprocket drive units are provided with reversible teeth to solve this problem. While this approach effectively increases the service life of the sprocket teeth, it suffers a number of drawbacks. First, it should be appreciated that the reversing of the individual teeth is a labor intensive and time consuming task. In fact, the high cost of labor and the associated down time of equipment resulting in lost production economically prohibit application of this procedure in commercial settings. Additionally, it should be appreciated that the individual teeth are prone to become loose when subjected to particularly high loads, such as commonly experienced during armored face conveyor operation. This problem is further exacerbated by the harsh operating environment in an underground mine. Accordingly, it should be appreciated that the concept of providing a sprocket with reversible teeth is not appropriate for many applications, including armored face conveyors.
U.S. Pat. Nos. 3,082,637 to Paxton, 4,043,214 to Westlake and 4,049,112 to Tyslauk all disclose sprocket assemblies including two-piece sprocket drive units which may be removed from cooperating hubs so as to allow ready replacement without removal of the hub from the driving shaft. None of these references specifically disclose or suggest the concept of reversing the orientation of the sprocket drive units. Further, it should be appreciated that the heavy loads and harsh environment, such as experienced by an armored face conveyor, would lead to the direct application of large forces and stress concentrations on the fasteners at the center joint holding the two-piece drive units together. The likely result is premature failure. Accordingly, it should be appreciated that a new approach is needed to provide a reversible sprocket for heavy duty applications, including armored face conveyors.